The present invention relates to a cross-linking agent (xe2x80x9ccross-linkerxe2x80x9d) for a negative photoresist, and a process for forming a negative photoresist pattern by using the same.
At present, most of the photoresist patterns used in a lithography process employing a light source of extremely short wavelength (250 nm or less) are positive types. However, xe2x80x9cID biasxe2x80x9dxe2x80x94i.e., the difference in CD (Critical Dimension) between an isolated line and a dense line in a photolithography pattern using the same exposing conditionxe2x80x94becomes important as semi-conductor devices shrink greatly in size. Accordingly, it is important to reduce ID bias in order to produce a device suitable for light sources with wavelengths of 130 nm or less. It is preferable to use a negative photoresist so as to reduce ID bias. However, it is not easy to prepare a polymer that is suitable for negative photoresists, and photoresist compositions thereof, for the following reasons:
(1) In order to prepare a negative photoresist composition, a photoresist polymer must be selected that has one or more functional group(s) that readily form cross-links in exposed regions and hardly forms cross-links in non-exposed regions. However, this selection is not easy.
(2) In the case of a negative photoresist composition, the photoresist polymer should become cross-linked upon light exposure. However, it is difficult to select an appropriate cross-linker which has such a function. For example, conventional cross-linkers absorb too much energy in the extremely short wavelength region of the light spectrum, in particular ArF radiation (193 nm).
(3) In order to reduce the production cost, conventional alkaline developing solution may be used in the developing process, but a negative photoresist composition generally has low solubility in the alkaline solution. Thus, it is difficult to form a minute pattern.
The object of the present invention is to provide negative photoresist compositions which are suitably used in a photolithography process employing a light source of extremely short wavelength, in particular, an ArF light source.
Another object of the present invention is to provide photoresist copolymers and cross-linkers that are suitable for preparing the negative photoresist composition.
Still another object of the present invention is to provide processes for preparing ultra-micro patterns using the photoresist composition.
In order to achieve these objects, the present invention provides a cross-linker having two or more aldehyde groups.
In addition, the invention provides a photoresist composition which comprises (i) a photoresist polymer comprising one or more alicyclic monomer(s) having hydroxyl group(s) (ii) a cross-linker having aldehyde groups, (iii) a photoacid generator and (iv) an organic solvent.